View of the Caracol and its platform. One of many round structures which began appearing in the Terminal Classic and the Early Postclassic periods, this one is surely the largest and most complex. While round structures have been associated with the cult of Quetzalcoatl (the Plumed Serpent) in Central Mexico, the Caracol was used as an observatory for sighting significant alignments of celestial bodies. This may not have been out of line with the cult of Quetzalcoatl, however, as two of his aspects were associated with Venus: one with the planet's appearance as Morningstar and one with its apperance as Eveningstar.